This invention relates to an optical fiber submarine cable forming a long-distance, optical fiber submerged repeater system in the field of optical communications using a low-loss optical fiber as a transmission medium.
The optical fiber has advantages of low loss, wide band and light weight and hence is regarded as a promising transmission medium which will succeed a coaxial submarine cable heretofore employed. The optical fiber is made of los-loss silica glass or optical glass, and hence is brittle and easily broken under an external force, such as bending or tensile force; and when the optical fiber is immersed is seawater for a long time, a very small crack in the glass is likely to grow, resulting in breakage of the optical fiber. Therefore, the optical fiber is usually coated with nylon or like material so as to enhance its mechanical properties and prevent their degradation. A submarine cable is laid as deep under the sea as 8000 m and exposed to a high pressure of about 800 kg/cm.sup.2 on the sea bottom. When the coated optical fiber is applied hydraulic or like pressure, the optical fiber is slightly bent due to nonhomogeneity of the coating material, causing a marked increase in transmission loss.
In view of the above, it has already been proposed to house the coated optical fiber in a high pressure resisting pipe for protecting the coated optical fiber from a high hydraulic pressure on the sea bottom. Further, in a long-distance, submerged repeater system, the electric power must be supplied to submerged repeaters; this requires the provision of a power supplying feeder in the submarine cable and an insulating layer for insulating the power supplying feeder. Moreover, tension resisting wires of large tensile strength are needed for the submarine cable so that it may not be broken when laid deep under the sea or drawn up for repair. In conventional optical fiber submarine cables, however, no consideration is paid to early attenuation of a surge which is caused by a short-circuit or opening trouble of the power supplying feeder.